This invention relates to improved delivery of topical local anaesthetic agents to an airway.
Adverse physiological response to laryngoscopy and intubation remains a significant problem of airway manipulation, both during anaesthesia and other diagnostic procedures. Tactile stimulation of receptors in the pharynx, hypopharynx, vocal cords and tracheal mucosa results in reflex gagging, coughing, bucking and laryngospasm as well as release of catecholamine (adrenaline and nor-adrenaline) and direct reflex sympathetic stimulation of the heart.
Clinical manifestations, other than the obvious motor responses, include a rise in pulse rate and blood pressure. These changes can be marked and are usually well tolerated by young healthy patients. However, in the elderly, premature neonates, or patients with cardiac or neurological disease, these haemodynamic changes, with concomitant increase in myocardial work and a decrease in cardiac output, can be critical and overcome the ability of a patient to compensate for existing disease.
Sensory block of the upper airway with an aerosolized, topical anaesthetic such as lidocaine, is possible using an ultrasonic nebulizer, an IPPB device or a compressed gas-powered jet nebulizer, and is clinically effective in blunting these responses. See, for instance, Christoforidis et al, Chest, 59 (6): 629-633 (1971); Vuckovic et al, Anesth. Analg., 59 (10): 803-804 (1980); Korttila et al, Acta Anaesth. Scanda. 25: 161-165 (1981); Kirkpatrick et al, Am. Rev. Respir. Dis., 136:447-449 (1987); Isaac et al, Anaesthesia, 45:46-48 (1990); and Foster et al, Am. Rev. Respir. Dis., 146:520-522 (1992). However, variable dosage loss due to an unsatisfactory delivery method, is disadvantageous. Therefore, there remains a need for an improved method of delivering a topical anaesthetic to a patient's airway.
Moreover, this prior art delivery technique is primarily reserved for procedures in awake patients as it requires patient cooperation, in particular active breathing, and is time consuming. Therefore, there remains a need for an improved method of delivering a topical anaesthetic to the upper airway of an unconscious or uncooperative patient without necessitating direct vision achieved by laryngoscopy.
Topical lidocaine spray currently available from ASTRA as "Xylocaine Endotracheal Aerosol" requires direct application under vision best achieved at laryngoscopy. The laryngoscopy is disadvantageously performed without prior airway topicalization, and intubation carried out at the time of laryngoscopy occurs too soon after the anaesthetic agent is applied for significant benefit to be achieved. The large droplet size of the current aerosol has been implicated in inducing airway irritation and even laryngospasm. Any technique such as spraying the trachea and vocal cords at laryngoscopy, that increases the duration and number of manipulations of the procedure has been shown to increase the stress response.
The Laryngojet technique of instilling liquid lidocaine directly into the trachea just before intubation does have small beneficial effect by blunting the early tracheal response to the tube, but has no effect on the initial response to laryngoscopy and intubation. Bronchodilator aerosol has been administered via the breathing circuit, to a mechanically ventilated patient intubated with an endotracheal tube.
General anaesthetic and induction agent dosages are limited by their adverse effects and must be titrated to a patient's individual requirements in order to achieve the correct depth of anaesthesia without haemodynamic compromise. Titration of the dose and timing of the airway, manipulation, in particular of an intubation, are necessary. A reliable, simple and reproducible method of blocking/blunting the physiological response to intubation would simplify anaesthetic induction and intubation.
Intubating a patient with an anaesthetized airway requires a significantly lighter plane of anaesthesia. The intubation could possibly be achieved safely and reliably under light general anaesthesia without muscle relaxation. Therefore, a method providing for reliable and rapid sensory block of the upper airway, would benefit this aspect of anaesthesia. Such a method would be especially advantageous if it could be used to provide reliable sensory block of the upper airway without direct vision achieved by laryngoscopy.